1. FIELD OF THE INVENTION
This invention relates to improvements in operability of an ion beam analyzing apparatus which analyzes composition and/or physical properties of a small area of an element, a product or the like using a high energy charge beam in various industrial fields including the technical field of semiconductors, the medical and biological technical fields and so forth, and more particularly to an ion beam analyzing apparatus wherein a scan image displayed on a display device and the shape of a beam spot of an ion beam can be made to coincide readily with each other.
2. DESCRIPTION OF THE PRIOR ART
As is well known in the technical field of semiconductors, an increase of the storage capacity and an increase of the information processing speed are demanded in order to process a large amount of information on a computer. To this end, development of high integration of ICs has been directed from LSIs to VLSIs and further to three dimensional ICs. As such development proceeds, individual elements, wires for those elements are remarkably reduced in size and increased in number of layers and besides use of a very shallow region under a surface is proceeding. Meanwhile, in development or process investigation of such ICs, an analysis of a distribution of atoms in a microscopic area is very important, and recently, the effectiveness of analyzing techniques such as the Rutherford backscattering method (RBS) and the particle excitation X-ray spectroscopic method (PIXE) which employ a converged ion beam of a high energy (MeV) have a resolution smaller than 1 .mu.m is recognized. Thus, improvement in function of an ion beam analyzing apparatus is being proceeded.
FIG. 6 schematically shows an exemplary one of a conventional ion beam analyzing apparatus. Referring to FIG. 6, the conventional ion beam analyzing apparatus is generally denoted at 51 and includes an ion source 53 disposed in an ion accelerator 52. A high energy ion beam 55 is generated from the ion source 53 of the ion accelerator 52 and accelerated by an accelerator tube 54 in the ion accelerator 52 has. The thus accelerated high energy ion beam 55 is then deflected, while passing through a deflecting analyzing electromagnet 56, normally by the angle of 15 degrees so that it is classified in ion type and energy. Subsequently, the high energy ion beam 55 is restricted to several tens .mu.m in diameter by an objective collimator 57 and then, after passing a drift space of several meters and deflecting electrodes 62, is introduced into two or three series of quadruple pole magnetic lenses 58. While the high energy ion beam 55 passes the quadruple pole magnetic lenses 58, it is converged at predetermined reduction ratios ( constants ) in the X and Y directions, which depend upon the quadruple pole magnetic lenses 58 and an optical layout dimension, and then it is irradiated upon a target 60 accommodated in a vacuum chamber 59, that is, upon a specimen on the target 60, so that it forms a beam spot on the specimen. Consequently, ions, electrons, photons and so forth are scattered and radiated from the specimen by a mutual action of the incident ion beam 55 and the target 60. Those particles are detected by means of a detector 61 and a secondary electron detector 63 provided in the vacuum chamber 59. A detection value detected by the secondary electron detector 63 is inputted to and displayed on an image apparatus (not shown).
In the ion beam analyzing apparatus 51, an ion beam 55 is deflected by the deflecting electrodes 62 interposed between the objective collimator 57 and the two series of quadruple pole magnetic lenses 58 so that it can be irradiated upon an arbitrary position of the specimen on the target 60 to form a beam spot in units of microns. Further, since the position of the beam spot is moved by applying a high frequency potential to the deflecting electrodes 62 or supplying a high frequency voltage to the deflecting electrodes 62 by way of manual operation of a manually operable mechanism (not shown), a certain preset area of the specimen on the target 60 can be scanned by the beam spot. Further, a two-dimensional surface analysis in the area can be performed by displaying a signal for analysis on a cathode ray tube in synchronism with the scanning position of the ion beam. It is to be noted that the deflecting electrodes 62 can be replaced with deflecting magnetic poles.
Meanwhile, since an ion beam is irradiated upon the target 60, secondary electrons are generated from the surface of the specimen supported on the target 60. However, since the intensity of the secondary electrons thus generated differs depending upon the profile of the surface of the specimen or the kinds of elements of the specimen if the beam irradiating conditions are identical, information conforming to the differences can be obtained.
Accordingly, a surface image equivalent to that obtained by a scanning microscope can be obtained by synchronizing the signal of the secondary electrons with the position of the beam spot, which depends upon a high frequency potential or a high frequency current, by way of scintillation and by means of a photomultiplier. Making use of this fact, upon analysis, the irradiation position of an ion beam is set in accordance with a surface scan image obtained from secondary electrons and the set position data are inputted to the deflecting electrodes at the position to effect setting of the position of the ion beam. Such an operation is normally performed by visually displaying and setting, while a surface image of the specimen obtained from secondary electrons is displayed on a cathode ray tube, the position information as a point on the cathode ray tube in accordance with the set image condition. Then, after such inputting, an ion beam is automatically positioned and irradiated at the position to collect data in order to make an analysis.
While the deflecting electrodes 62 in the conventional ion beam analyzing apparatus described above is interposed between the objective collimator 57 and the quadruple pole magnetic lenses 58, they are sometimes disposed at some other positions. Referring to FIG. 7, there is shown another exemplary one of conventional ion beam analyzing apparatus. In the second conventional ion beam analyzing apparatus, the deflecting electrodes 62 are disposed between the quadruple pole magnetic lenses 58 and the vacuum chamber 59 so that an ion beam converged by the quadruple pole magnetic lenses 58 is deflected by the deflecting electrodes 62 and introduced to the target 60 in the vacuum chamber 59.
U.S. Pat. No. 5,063,294 discloses a converged ion beam apparatus which makes a prior art document to the invention of the present application. An objective slit device of the electrostatic capacitance type for detecting a width of a variable aperture is disclosed in Japanese Patent Laid-Open Application No. Heisei 2-281546. A build-up type high precision quadruple pole magnetic lens is disclosed in Japanese Patent Laid-Open Application No. Heisei 2-244547. A correcting method for an error of the direction of rotation of a beam by a quadruple pole magnetic lens is disclosed in Japanese Patent Laid-Open Application No. Heisei 2-256147. A monitoring method for an RBS analysis and/or a PIXE analysis using a secondary electron image is disclosed in Japanese Patent Laid-Open Application No. Heisei 3-238743. A vacuum vessel in which a plurality of specimens can be accommodated is disclosed in Japanese Patent Laid-Open Application No. Heisei 3-261058. An apparatus wherein a plurality of semiconductor detectors are employed and detection signals of them are added in order to decrease the measuring time is disclosed in Japanese Patent Laid-Open Application No. Heisei 3-81938.